In conventional wireless communication systems such as High Speed Downlink Packet Access (HSDPA) systems, the High Speed Shared Control Channel (HS-SCCH) carries downlink signaling information required for demodulating the High Speed Downlink Shared Channel (HS-DSCH). Since power control for the HS-SCCH is defined generally in 3GPP specifications as being under control of the serving Node B transceiver, the operator of the Node B transceiver is free to implement any power control algorithm. Traditional R99 power control and related methods allow for a relatively simple power control technique which couples the HS-SCCH transmit power with a downlink Dedicated Physical Control Channel DPCCH through the use of an offset factor. Since the control channel is always on, the Node B transceiver simply applies the offset factor to the present DPCCH power to arrive at the transmission power of the HS-SCCH when there is packet data to be transmitted on the HS-DSCH.
Although the use of an offset factor, as described, is relatively easy to implement, performance of the HS-SCCH can degrade severely when the UE is in a soft-handover (SHO) state because HSDPA-related channels are not in soft-handover. Due to diversity combining gains, the dedicated channels require much less power when engaged in SHO. However, the HS-SCCH still has identical power requirements as in the non-SHO case, leading to poor performance when R99 power control algorithm is used, especially when the SHO occurs at low UE speeds. For example, when the UE is in 2-way SHO, approximately 5 dB more power may be required on the HS-SCCH to reach 1% FER due to degradation from the R99 power control algorithm.
In some instances, power control can be improved by basing downlink power control on uplink oriented information such as the Channel Quality Indicator (CQI) report. Drawbacks exist for CQI based power control in that the CQI report, for example, in HSDPA systems is issued at a frequency not greater than 500 Hz. As a result conventional CQI based power control is rendered ineffective for UE speeds of around 30 km/h or greater or for other scenarios where the frequency of the CQI report is relatively low or slow.